Evan G., Jeff K., Heather F.

The time for re-calibration of the End Y Pcal PD calibration has elapsed. In addition, we wanted to determine if the calibration of the EY RX PD has been impacted by the observed--and fixed--clipping (see LHO aLOGs 33108 and 33187). This was checked by making a new round of power calibration measurements. The new report is attached (first attachment).

While there, as preventative maintenance we decided to align the outer beam so that it entered the integrating sphere aperture closer to the center. Attached are a before and after images showing this adjustment. 

At the end station, we thought that the measurements were looking good from the spot checks, but only upon getting back to the corner station and using the full suite of Pcal Matlab analysis scripts did we find an issue. The full-data of the working standard had especially weird behavior for two of the measurements (see attachments, especially pcal_endy_20170117_2.png). Consulting with Darkhan T., he suggested that if any other electrical equipment is plugged into the same outlet as the working standard current amplifier, then there can be added noise or glitches in these measurements.

This is unfortunate, but the report indicates the RX/WS ratio (corrected for optical efficiency) has not changed significantly for either of the Pcal beams. Perhaps this is because added noise is sufficiently averaged such that the impact is small. The measurements are only partially conclusive, but they suggest that the calibration has not been impacted by the clipping issue.

The bottom line is that the measurement is not as clean as we would like, and so we would like to repeat this measurement next week to gain confidence in the calibration.